This project will employ structural (MRI) and functional (fMRI) neuroimaging techniques to examine the neural basis of selected social cognitive, affective, and executive functioning deficits, and ritualistic-repetitive behaviors, in autism. Social deficits and ritualisticrepetitive behaviors are defining features of autism, and deficits in social cognition (e.g., processing emotional and social cues reflected in facial expressions) and executive function (e.g., generating flexible task-appropriate actions while inhibiting task-inappropriate ones) are considered key neuropsychological processes underlying these behaviors. Despite progress in describing these deficits, their neurobiological bases are still largely unknown. We propose to explore the neural circuitry of social cognitive, affective, and executive function processes and ritualistic-repetitive behaviors in autism in four studies designed to: (1) characterize the neural circuitry underlying inferences of social intentionality in autism, (2) examine neural circuitry underlying the processing and appreciation of facial expressions in autism, (3) explore the neural circuitry supporting the initiation and inhibition of taskappropriate/inappropriate behaviors in autism, and (4) characterize the structural integrity and development of frontal-striatal tracts, which we hypothesize to be involved in ritualistic-repetitive behaviors associated with autism. These aims will be addressed in three fMRI studies involving high functioning autistic adolescent and adult males, and in one longitudinal study employing diffusion tensor imaging in a sample of autistic children (ages 2- to 4-years). This project links conceptually to Family Study Project, Mouse Genetics Project, Fragile X Project, and Treatment Project, where these same processes are examined, as well as to a companion, separately funded study of these neuropsychological processes in this same sample of autistic individuals. This project brings together several experienced neuroimaging researchers, new to autism, forming the basis for the development of an integrated program of neuroimaging research to characterize key elements in the neural circuitry of autism. This information should further our understanding of the neural mechanisms as well as refine our notions of the brain and behavioral phenotypes in this disorder.